The present invention concerns a process for removing impurities, particularly liquids and/or particles, from liquid-contaminated or wetted surfaces, and of especially plate-shaped workpieces, using at least one wiping element, in which a relative movement is carried out between the surface and the wiping element and the wiping element contacts the surface and/or the liquid layer forming or containing the impurities.
The present invention further concerns an apparatus for removing impurities, particularly liquids and/or particles, from liquid-contaminated or wetted surfaces, and especially plate-shaped workpieces, using at least one wiping element, in which a relative movement is permitted between the surface and the wiping element. The wiping element contacts the surface and/or the liquid forming or containing the impurities thereon. At least one endless rotating wiping element that is guided around reversing rollers is provided which includes a cleaning run for acting on the surface to be cleaned and a return run directed opposite to the cleaning run.
For example, in the automobile industry, but also in the manufacture of kitchen appliances, flat sheet or metal panels are shaped in stamping lines. For such shaping, it is advantageous if the panels exhibit a uniform or targeted lubrication of the surface, e.g., with oil. In addition, the surface should be as free as possible of foreign bodies, pile, fluff, grit, dust, and/or solid particles. Any foreign bodies or particles that may arise through production processes, for example, cutting processes or aligning or stacking processes, can be deposited on the surfaces of the panels leading to surface defects, scratches, pitting, etc., which are a problem especially after painting.
Especially as a result of increased use of galvanized-steel panels, stainless-steel panels, as well as aluminum panels, the damage to surfaces by particles or drawing defects as a result of improper oiling becomes more of a problem. In practice, dirty panels lead to refinishing in up to a quarter of the exterior body panels (for example, doors, roof, trunk, etc.) of a motor vehicle.
For the manufacturing process, there is thus the problem of having to clean such panels appropriately prior to feeding into stamping lines, be it in the automobile industry, in the manufacture of panels in the kitchen- and household-appliance industry, etc.
Until now it has been known to use washing machines working with water or wash oil and possibly high-pressure nozzles, in which it is possible to add detergents. This process can be supported by rotating brushes. Drying of the workpieces or panels proceeds with the aid of squeegee rolls or via blowing off of the surfaces. In addition, washing machines are known which operate exclusively with oil. These can be employed if oiling of the surface is necessary for the drawing process following the cleaning step.
On the whole, however, one is dealing in the case of these washing machines and washing units with expensive equipment. Beyond this, there is a problem with the disposal of the used wash water.
Rotating wiping elements with a cleaning run and a return run are known, for example, from DE 42 13 342 A1 or from DE 43 14 046 C2. Therein, processing of the surfaces proceeds in the dry state. Cleaning of a surface contaminated or wetted with liquid is hardly or only to a limited extent possible using the apparatus according to DE 42 13 342 A1.
DE 43 14 046 C2 describes a process for cleaning dry surfaces in which the wiping element is moistened. Both this process as well as the corresponding apparatus are thus not suited to cleaning surfaces contaminated or wetted with liquid.
The problem therefore exists to create a process and apparatus of the type mentioned above with which it is possible to remove particles from surfaces contaminated or wetted with liquid, while avoiding washing machines operating with water or oil.
The process of the type mentioned above for solving this problem is surprisingly characterized by the fact that the wiping element or elements are cooled down with respect to the surroundings, the workpiece, and its contamination, and the surface to be cleaned is acted on by the comparatively cold wiping element or elements.
The present invention makes use of the fact that liquids are precipitated onto a cold surface as condensate or, at an appropriately low temperature of this surface, are even deposited as a solid. Thus, if one passes the cooled wiping element, e.g., a brush, over the surface contaminated or wetted with liquid, the moisture will become deposited on the wiping element given an appropriate temperature of the latter. In the case of the oils normally adhering to the workpieces to be cleaned, there is additionally the fact that their viscosity increases with decreasing temperature. Thus, there results a type of sticking effect between the cold wiping element and the liquid. The process according to the present invention can be appropriately influenced with regard to the applied temperature depending on whether one would like to remove more or less liquid from the surface. Above all, the particles located in a liquid film can also be deposited or xe2x80x9cfrozenxe2x80x9d onto the wiping element such that these particles can be removed with correspondingly high certainty without it being necessary to include an expensive washing process using water or oil, which, for its part, would have to be cleaned away again.
An especially favorable and advantageous embodiment of the present invention is provided by the fact that at least the surface of the workpiece to be cleaned is heated up prior to contacting with the wiping element. Thus, there exists the possibility for modifying the cleaning process through temperature control. For example, a short-term rapid heating of the surface to be cleaned and possibly even to be dried can warm and even instantaneously heat the liquid adhering to this surface and thus reduce its viscosity. If such a thinned and heated liquid film meets up with the cooled and possibly extremely cold wiping element, the liquid freezes to the surface of the wiping element. As a result, dirt particles located in the liquid are also picked up and taken along by the wiping element. Appropriately thorough cleaning can be attained as a result.
One can attain a large temperature differential with correspondingly strong cleaning effect when the cleaning element is cooled down at least in the area acting on the surface to be cleaned almost to the solidification temperature, to the solidification temperature, or even below the solidification temperature of the liquid contaminating or wetting the surface being acted on.
This increases the effect of the liquid adhering or even xe2x80x9cfreezingxe2x80x9d to the cleaning or wiping element.
It can be appropriate for the cleaning or wiping element to be cooled down such that it is about 10xc2x0 C. or more, for example, on the order of magnitude of about 20xc2x0 C. or more colder than the surface to be cleaned or the liquid wetting this surface. Tests have shown that a good cleaning effect is attained at such a temperature differential.
Embodiments of the process according to the present invention are contained in claims 5-10.
Claim 5 specifies, for example, an advantageous technique concerning the movement of the workpiece and its heating up as well as the contact with the cold wiping element after the point of heating.
Claim 6 contains an expedient contacting of the workpiece with the wiping element perpendicular to the direction of feeding of the workpiece.
Claim 7 concerns the removal of impurities picked up by the wiping element, which can advantageously occur outside the cleaning area.
Claim 8 contains an especially favorable embodiment of the process according to the present invention to the effect that following the cleaning process, a wetting liquid, for example, an oil can again be applied via the wiping element provided for cleaning to the cleaned workpiece so that the latter is well prepared for a subsequent shaping or stamping process and/or the wiping element is nicely conditioned for good pickup of further particles.
Claim 9 provides appropriate procedures for cleaning the wiping element.
Claim 10 contains a possible embodiment of the process in which the heat arising during refrigeration can be utilized in the cleaning process according to the present invention, namely, at least partially in heating up the surface to be cleaned before contacting the surface, viewed in its feeding direction, with the wiping element.
Above all, upon combination of a few or several of the above-described process features and measures, a cleaning of surfaces contaminated or wetted with liquid and particles contained therein is obtained, without the need for expensive washing and rinsing processes as well as the corresponding equipment investment and additional costs for detergent and disposal of wash water.
The above-mentioned apparatus for carrying out the process is, in solving the posed problem, characterized by the fact that it exhibits a cooling device for cooling down at least the cleaning run. Thus, in the above-mentioned apparatus, a cooling device or refrigerator is installed which cools down at least the cleaning run of the wiping element in suitable fashion so that this element can provide for an appropriate increase in the viscosity of the liquid located on the surface and can take along this liquid together with the particles contained therein.
Here, it is expedient if a feeding device is provided for a plate-shaped workpiece and the cleaning or wiping element or elements are positioned to act perpendicularly to the feeding direction. As a result, the desired relative movement between workpiece and wiping elements can be attained in simple fashion so that especially the workpiece can best follow the overall tempo of the production line and still be cleaned prior to its actual processing. In addition, the dirt picked up by the wiping elements can be moved in this manner away from the workpiece off to the side.
The wiping element or elements can be positioned in a refrigerated tunnel serving to cool down at least the cleaning run, the tunnel being open toward the surface to be cleaned. Such a refrigerated tunnel, in which a considerably reduced temperature thus prevails, can cool down the wiping element or at least its cleaning run in the desired fashion without adversely affecting accessibility to the surface to be cleaned.
It is especially favorable if the cooling device, appropriately the refrigerated tunnel mentioned above, also surrounds or acts on the wiping element at least over a portion of its return run. In this way, still more heat can be removed from the rotating wiping element. In addition, the cold can be more effectively employed in such a design, and the danger that, for example, warm air will be carried by the wiping element, itself, into the cooling device can be reduced.
A heating device for the surface to be cleaned, for example, a channel running perpendicular to the feeding direction and incorporating at least one heat source such as a quartz lamp, heating rods, gas flame, or the like can be positioned ahead of the cooling device in the feeding direction, and the heater or heating device and the cooling device or refrigerated tunnel can be positioned one right after the other in the feed direction. In this way, one can carry out appropriate heating up of the liquid wetting the surface of the workpiece to be cleaned or heating up of this surface immediately prior to contact with the cold wiping element. A heating up of the entire workpiece can be avoided since it is only important that the portion of the surface to be cleaned which is directly acted on by the wiping element be appropriately warmed or heated just prior to the wiping action.
One can provide as wiping element one or more linear brushes such as are known, for example, from DE 43 14 046 C2 (FIG. 3), and in the area outside of that travelled by the workpiece, cleaning devices, for example, doctor blades, at least one heating device, and/or blowing nozzles can act on the wiping element such that the previously picked-up impurities can be removed again in this area. Here, a heating device can reliquefy the previously picked-up and frozen liquid so that it can be more readily doctored, centrifuged, and blown off.
In the direction of rotation of the wiping element, behind the cleaning area, thus suitably on its return run, one can position at least one apparatus for wetting the wiping element, especially the bristles, with a liquid, for example, a lubricating liquid such as oil or the like. In this way, a cleaned surface can be simultaneously intentionally oiled again by the cleaning element either in order to be able to carry out another cleaning step including the already mentioned cooling down at a subsequent cleaning or wiping element in the feeding direction (in order to be able to remove all of the previously present particles with still greater reliability) or in order to prepare the workpiece for a shaping process. The capacity of a single wiping element or an initial wiping element in the feeding direction for picking up the particles to be removed can also be improved through such wetting.
Especially upon use of several successive wiping elements in the feed direction, these elements can have opposing wiping directions. In addition, the wiping elements can also be formed by tiles. The picked-up liquid, usually oil, can be reused following cleaning of the wiping element or elements. For example, this liquid, following appropriate filtering, could be fed back to an oiling device used in preparing panels for shaping or drawing.